Oxford University Press | Online Resource Centre

Choose your answers from a-e by clicking the radio button next to each choice and then press 'Submit' to get your score.

Question 1

In flies, frogs, and chicks, gradients of morphogens determine the future antero-posterior and dorso-ventral axes of the developing embryo. How is the antero-posterior axis determined in C. elegans?

a) Bicoid protein is translated in the anterior of the fertilized egg, leading to a gradient that determines the antero-posterior axis.

b) Nodal triggers formation of an organizer that will determine the dorsal, and hence the anterior, side of the embryo.

c) Opposing gradients of chordin and BMP-4 establish the antero-posterior axis.

d) β-catenin becomes localized to the nucleus in the future anterior cells after fertilization.

e) Sperm entry leads to a reorganization of the cytoskeleton and redistribution of maternally packaged PAR proteins, which in turn determine the antero-posterior axis.

Question 2

Do HOX genes play a role in the development of C. elegans?

a) No, C. elegans does not have HOX genes.

b) No, C. elegans has HOX genes but none of them are used during development.

c) Yes, C. elegans has 4 clusters of HOX genes, just like mammals, that are required for specification of the identity of structures during embryogenesis.

d) Yes, but only one HOX gene is required in the embryo; the others provide positional identity in the larva.

e) Yes, and their genetic organization and role in development is nearly identical to that in Drosophila.

Question 3

What are the lin-4 and lin-14 genes of C. elegans?

a) Lin-4 encodes a miRNA that represses lin-14 translation, which in turn regulates the timing of larval development.

b) Lin-4 and lin-14 are genes that are named for their control of the first division, and hence the lineage of the AB and P1 cells.

c) Lin-4 and lin-14 are C. elegans versions of the HOX genes.

d) Lin-4 and lin-14 both encode miRNAs that serve as cell-cell signaling molecules in C. elegans.

e) Lin-4 controls the timing of transcription of lin-14, and so is referred to as a 'heterochronic' gene.

Question 4

The ability of the sea urchin embryo to regulate its development illustrates the fact that there are maternally-determined differences along the animal-vegetal axis that are necessary for normal development. Which of the following statements about regulation in sea urchin embryos is consistent with that fact?

a) Up until the hatching of the embryo as a pluteus larva, any blastomere can be separated from the others and will regulate to go on and develop into a fully formed and full sized larva.

b) Up until the hatching of the embryo as a pluteus larva, any blastomere can be separated from the others and will regulate to go on and develop into a fully formed, yet smaller, larva.

c) Blastomeres from the animal or vegetal poles of the embryo can be isolated and will go on to form an embryo, as long as either an animal or vegetal pole is included.

d) Blastomeres at the 4-cell stage each still possesses a portion of the original animal-vegetal axis, and if isolated will go on to form a fully formed, yet smaller, larva.

e) Any Blastomeres at the 8-cell stage can still regulate to form a full larva, but by the 60-cell stage, blastomeres will develop according to their presumptive fate.

Question 5

In which way is the organizer region of the sea urchin similar to that in frogs?

a) The organizer induces the dorso-ventral axis.

b) The organizer forms near the dorsal lip of the blastopore.

c) The organizer accumulates β-catenin, which in turn activates the expression of cell-cell signaling molecules.

d) The organizer will become the mesoderm.

e) The organizer will express high levels of nodal.

Question 6

Which one statement best describes gastrulation in sea urchins?

a) Gastrulation is initiated by invagination of the micromeres at the vegetal pole.

b) The mouth of the pluteus larva will form from mesomeres on the oral side of the 60-cell embryo.

c) The gut will form from the macromeres at the 16-cell stage.

d) Mesenchymal cells originating at the vegetal pole will invaginate first during gastrulation and will form skeletal structures in the pluteus larva.

e) All of the above are true.

Question 7

In the ascidian, Styela, the yellow pigmented myoplasm marks cells fated to become muscle cells in the tail; however, at the molecular level, the key determinant of tail muscle seems to be:

a) localization of β-catenin to the nuclei in the vegetal portion of the embryo.

b) the sperm centrosome.

c) the gene product of macho-1 gene.

d) expression of the Brachyury gene.

e) induction of muscle by FGF gene.

Question 8

The role of the Brachyury gene in ascidians is similar to that in Xenopus in that:

a) Brachyury sets up the animal-vegetal axis.

b) Brachyury is characteristic of the organizer region.

c) The Brachyury gene is expressed specifically in those cells that will form somites, and hence muscle.

d) Signaling that leads to induction of the mesoderm results in expression of the Brachyury gene in the mesoderm.

e) Brachyury is the master switch gene for muscle development on both organisms.

Question 9

Which statement describes Dictyostelium?

a) Dictyostelium cells can live as single, free-living cells, until they are stimulated by starvation to aggregate and sporulate.

b) Dictyostelium is a fungus that forms a cap with spores, like a mushroom.

c) Dictyostelium is a plant that forms a fruiting body instead of a flower.

d) Dictyostelium is related to snails and other slugs that have evolved from snails through loss of their shells.

e) Dictyostelium is most closely related to bacteria.

Question 10

What is the role of cAMP in Dictyostelium development?

a) cAMP induces differentiation of cells as prestalk cells.

b) cAMP is secreted by individual cells in response to starvation, and serves to attract nearby cells resulting in formation of aggregate.

c) cAMP signals lead cells to express DIF-1, which in turn stimulates aggregation.

d) cAMP is used as an energy source for migrating Dictyostelium cells.

e) cAMP activates the Wnt pathway and leads to localization of β-catenin.

Oxford University Press, Online Resource Centre, Chapter 05.

Chapter 05

Instructions